Martian Atmospheric Temperature and Density Profiles During the First Year of NOMAD/TGO Solar Occultation Measurements

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We present vertical profiles of temperature and density from solar occultation (SO) observations by the “Nadir and Occultation for Mars Discovery” (NOMAD) spectrometer on board the Trace Gas Orbiter during its first operational year, which covered the second half of Mars Year 34. We used calibrated transmittance spectra in 380 scans, and apply an in-house pre-processing to clean data systematics. Temperature and CO2 profiles up to about 90 km, with consistent hydrostatic adjustment, are obtained, after adapting an Earth-tested retrieval scheme to Mars conditions. Both pre-processing and retrieval are discussed to illustrate their performance and robustness. Our results reveal the large impact of the MY34 Global Dust Storm (GDS), which warmed the atmosphere at all altitudes. The large GDS aerosols opacity limited the sounding of tropospheric layers. The retrieved temperatures agree well with global climate models (GCM) at tropospheric altitudes, but NOMAD mesospheric temperatures are wavier and globally colder by 10 K in the perihelion season, particularly during the GDS and its decay phase. We observe a warm layer around 80 km during the Southern Spring, especially in the Northern Hemisphere morning terminator, associated to large thermal tides, significantly stronger than in the GCM. Cold mesospheric pockets, close to CO2 condensation temperatures, are more frequently observed than in the GCM. NOMAD CO2 densities show oscillations upon a seasonal trend that track well the latitudinal variations expected. Results uncertainties and suggestions to improve future data re-analysis are briefly discussed. © 2022 The Authors. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.
The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCI through the ‘Center of Excellence Severe Ochoa’ award for the Instituto de Astrofísica de Andalucia (DEV-2017-0709) and funding by grants PGC2018-101836-B-100 (MCI/AEI/FEDER, EU), PID2019-110689RB-I00/AEI/10.13039/501100011033, and RTI2018-100920-J-I00. ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELLS), with the financial and contractual coordination by the ESAU Prod ex Office (PEA 4000103401, 4000121493) as well as by UK Space Agency through Grant ST/V002295/1, ST/V005332/1 and ST/S00145X/1 and Italian Space Agency through Grant 2018-2-HHS.0. US investigators were supported by the National Aeronautics and Space Administration. This work was supported by the Belgian Funds de la Recherche Scientific—FIRS under Grant 30442502 (ET_HOME). This project has received funding from the European Union Horizon 2020 research and innovation program under grant agreement No 101004052 (Road Map project).
With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).